A control device has been so far available which holds information indicating a time period in which a unit price of power is less expensive according to a midnight power rate system or a time-of-day power rate system, and gives an electric appliance an instruction to operate in the time period in which the unit price of power is less expensive (see Patent Literatures (PTLs) 1 and 2, for instance).
It is to be noted that the electric appliance is, for example, a home appliance such as a washing and drying machine and a dish washing and drying machine, or a heat pump water heater, which are provided in an ordinary family house.
There is a case where the control device is provided as part of such an electric appliance.
There is also a case where the control device is provided outside of the electric appliance. For instance, examples of the control device outside of the electric appliance include a control device that communicates with at least two electric appliances provided in a house and gives each of the at least two electric appliances an instruction based on a cost of the electric appliance.